In areas without public sewers, local and regional zoning laws typically limit building to sites where a standard septic system, i.e. a septic tank and leaching or disposal field, can be installed. In such areas, the subsoil conditions provide adequate percolation to treat wastewater.
Standard systems, however, are not intended to substantially remove nitrogen in the form of ammonia or nitrates, which typically enter the groundwater with the effluent.
Frequently, even where the geologic conditions might allow the use of standard septic systems, increasingly stringent regulatory standards require the removal of nitrogen from the wastewater.
Where standard systems cannot be employed, because of subsoil conditions, minimal lot size or regulatory restrictions, innovative on-site waste disposal systems have been used.
One type of on-site system involves waterless toilets which either compost or incinerate wastes. Since standard septic treatment systems are still required for the treatment of other household wastes ("graywater"), such systems typically mean additional costs to the landowner, as well as increased maintenance.
Another on-site system involves intermittent, pressurized dosing of standard septic tank effluent to the septic field. While the effluent from such systems have been shown to have reduced nitrates, it is difficult to determine the effectiveness of such treatment in a field installation where it is inconvenient or impossible to measure the nitrate level in the effluent.
Another on-site system is commonly referred to as the "Ruck"system. Wastewater from the toilet, or "blackwater", is initially separated from the graywater from showers, sinks, and washing machines. The blackwater is filtered through a sand bed. After a solids settling tank, the graywater is combined with the filtered blackwater and directed into a tank filled with rocks. Bacteria on the surface of the rocks convert the nitrates in the combined effluent into nitrogen gas which is vented. The effluent then flows into a standard septic field where it percolates into the ground.
One problem typically encountered with such a system however, is that it is not always certain that the combined wastewater will provide the proper balance of components necessary to allow complete bacterial conversion of nitrogenous material to ventable gas.